This invention relates, in general, to high voltage protection circuitry for an integrated circuit, and more particularly, to Electrostatic Discharge (ESD) Protection for an Input/Output (I/O) circuit of an integrated circuit.
The Input/Output (I/O) circuitry of an integrated circuit is the interface circuitry between circuitry external to the integrated circuit and circuitry internal to the integrated circuit. Input circuitry buffers incoming signals for the internal circuitry of the integrated circuit. Output circuitry buffers signals from the internal circuitry of the integrated circuit and typically comprises power transistors for driving large capacitive loads (for example, a bus line).
Static Discharge is common to any component that is handled. An Electrostatic Discharge (ESD) event to an integrated circuit can couple thousands of voltages to the integrated circuit. An ESD event is coupled through I/O circuitry since it is the interface between the internal circuitry of the integrated circuit and the external world. An ESD event is indiscriminate in its entry to the integrated circuit. The ESD event is coupled to any I/O circuit of the integrated circuit or between I/O circuits of the integrated circuits.
ESD protection circuitry is incorporated in I/O circuitry of an integrated circuit. The ESD protection circuitry dissipates an ESD event before harmful voltages or currents can damage circuitry of the integrated circuit. A problem with ESD protection circuitry is the protection mechanism is process dependent. Both the breakdown mechanism (due to an ESD event) of a device in the I/O circuitry and the point at which the ESD protection circuitry is enabled will vary depending on process variations. The ESD protection circuitry is often compromised to take into account all the different variations that could occur.
A second problem with ESD protection circuitry is protecting for all possible ESD events. Both positive and negative ESD events can occur. An ESD event can be coupled to a single pad or between pads of an integrated circuit. Power supply pads will couple an ESD event to all I/O circuitry. Most ESD protection schemes do not provide adequate protection due to area constraints or limited protection devices.
It would be of great benefit if an ESD protection circuit could be provided that is process independent and provides protection from most ESD events that can occur on an integrated circuit.